1. Field of the Invention
The invention generally relates to a scanner module for use in an optical scanner, for example, a bar code scanner.
2. Description of the Related Art
A typical optical scanner (for example a bar code scanner) has a light source, preferably a laser light source, and means for directing the laser beam onto a symbol (for example a bar code) to be read. On route to the symbol, the laser beam is generally directed onto, and reflected off, a light reflecting mirror of a scanning component. The scanning component causes oscillation of the mirror, so causing the laser beam repetitively to scan the symbol. Light reflected from the symbol is collected by the scanner and detected by a detector such as a photodiode. Decode circuitry and/or a microprocessor algorithm is provided to enable the reflected light to be decoded, thereby recovering the data which is recorded by the bar code symbol.
Scanners of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 4,409,470; 4,808,804; 4,816,661; 4,816,660; and 4,871,904, all of which patents have been assigned to the same assignee as the present invention, and all of which are hereby incorporated by reference.
In recent years, it has become more common for bar code scanners to have within them a distinct scanner module containing all the necessary mechanical and optical elements needed to create the scanning of the laser beam and to deal with the incoming reflected beam from the bar code that is being scanned. Using a separate scanner module, within the housing of the bar code scanner, facilitates a modular approach to design and manufacture, thereby keeping costs down, improving reliability, and facilitating the transfer of scanning technology to a variety of scanner housings. A typical prior art scanner module is disclosed in U.S. Pat. No. 4,930,848, to Knowles.
There are a large number of known ways of mounting a mirror within the scanning component to cause the necessary scanning motion of the laser beam. Some provide for oscillation in only a single direction, so that the scanning laser beam traces out a single path across the bar code being scanned. Others provide two dimensional scanning patterns, such as for example raster patterns or patterns of greater complexity. Examples of scanning components allowing two dimensional scanning are shown in U.S. Pat. No. 5,280,165, and in European Patent Application 540,781. Both of these are assigned to the same assignee as the present invention, and are hereby incorporated by reference.
As optical scanning systems have become more complex, and as the demand for smaller size and lower power consumption has increased, shock protection for the scanner modules has become more difficult. These highly efficient scan engines, with both resonant and nonresonant scanning elements are difficult to protect because the scanning element must be free to move for scanning but must be protected in the event of a shock (for example if the user drops the bar code scanner within which the scanner module is incorporated). Also, as sizes are reduced manufacturing tolerances begin to have more significant impacts on costs. Furthermore, it becomes more difficult to achieve accurate optical alignment during assembly and to maintain that optical alignment during the life of the product.